Light Scattering Intensity Measurements Research Articles

Online monitoring of dopamine particle formation via continuous light scattering intensity measurement

Using time resolved total intensity light scattering a two phase process was found in the conversion of 2-(3,4-dihyroxyphenyl)ethylamine, dopamine (DP), into microparticles. Phase 1 appears to involve oxidation of the DP, and may also include oligomerization below the light scattering threshold of detectability. After a certain lag time, the ‘Phase 1 Period’ (P1P), dependent upon reaction conditions, the light scattering increases sharply, heralding the onset of Phase 2. Precipitating particles are eventually formed in latter Phase 2. The solution goes through a series of color changes throughout Phase 1 and 2, starting as pink in Phase 1, and culminating in black particles in Phase 2. The reaction proceeds under virtually any conditions; purged with O2 or N2, unpurged, stirred or unstirred, under different pH conditions, etc. Stirring, increasing temperature, and adding potassium persulfate (KPS), all accelerate the reaction. P1P varied over nearly four orders of magnitude, from 10 s (pHinitial = 9.5) to 8 × 104 s (T = 25 °C, no pH control). Arrhenius behavior is found for P1P with low activation energies in the range of 10–25 Kcal/Mole. The precipitating particulates rapidly formed in Phase 2 suggest that they may involve non-covalent associations of oligomers formed in Phase 1, possibly due to loss of oligomeric solubility, in addition to possibly involving covalent polymer branching and cross-linking. Non-covalent aggregation of oligomers formed in Phase 1 seems most likely.

A Review of Experimental Techniques for Measuring Micro- to Nano-Particle-Laden Gas Flows

Dispersed micro- to nano-particle-laden gas flows are common in many engineering and environmental applications. Characterizing both their dispersed and carrier phase using experimental methods is very important for determining their properties and behavior. This paper reviews techniques for measuring the carrier phase, as well as the dispersed particles ranging from the micro- to the nano-scale. We focus not only on the developments of specific techniques over the last 20 years, but also on relationships and comparisons among these techniques. In addition to a systematic description and classification of these methods, we discuss the parameters they measure, such as particle velocity, size, composition and concentration. A more detailed review is provided for several important measurement techniques, including particle image velocimetry, the phase-Doppler particle analyzer and light-scattering intensity measurements for microparticles, as well as the scanning mobility particle sizer, the fast mobility particle sizer and the electrical low pressure impactor for nano-particles. The founding principles, development histories, various applications of these techniques and where they are going are summarized. This article provides a resource for investigators that plan to study micro- or nano-particle-laden gas flows in various contexts.

Measurement of Dynamic Light Scattering Intensity in Gels

In the scientific literature little attention has been given to the use of dynamic light scattering (DLS) as a tool for extracting the thermodynamic information contained in the absolute intensity of light scattered by gels. In this article we show that DLS yields reliable measurements of the intensity of light scattered by the thermodynamic fluctuations, not only in aqueous polymer solutions, but also in hydrogels. In hydrogels, light scattered by osmotic fluctuations is heterodyned by that from static or slowly varying inhomogeneities. The two components are separable owing to their different time scales, giving good experimental agreement with macroscopic measurements of the osmotic pressure. DLS measurements in gels are, however, tributary to depolarised light scattering from the network as well as to multiple light scattering. The paper examines these effects, as well as the instrumental corrections required to determine the osmotic modulus. For guest polymers trapped in a hydrogel the measured intensity, extrapolated to zero concentration, is identical to that found by static light scattering from the same polymers in solution. The gel environment modifies the second and third virial coefficients, providing a means of evaluating the interaction between the polymers and the gel.

Optical properties of polystyrene black dyed microspheres

The light absorption cross section is one of the most important optical properties along with the light scattering and the light extinction cross sections. The light scattering cross section when added to the light absorption cross section produces the light extinction cross section. Light absorption cross sections of polystyrene black dyed microspheres were measured by a multi angle absorption photometer (MAAP) together with the combination of a differential mobility analyzer (DMA) and a condensation particle counter (CPC). The MAAP is a filter based instrument that can measure light absorption properties without artifacts by using backward light scattering intensity measurements to compensate. Preliminary result for the 980 nm sized polystyrene black dyed microspheres depicts that the absorption cross section is about 1.5 × 10−14 m2 per sphere. In addition, the light absorption cross section of 233 nm and 10 μm spheres were measured. The near field scattering image data are shown for three polystyrene black dyed microspheres. The implication of the optical properties for the different sized black spheres is that the absorption coefficient and scattering image data depend on the size of the spheres.

Electrostatic Interaction and Complex Formation between Gum Arabic and Bovine Serum Albumin

The interaction of gum arabic (GA) and bovine serum albumin (BSA) has been investigated through turbidity and light scattering intensity measurements and by the use of dynamic light scattering, laser Doppler velocimetry, and isothermal titration calorimetry. It has been shown that GA and BSA can form soluble and insoluble complexes depending on the solution pH and the mixing ratio and is a function of the net charge on the complex. Soluble complexes were obtained when the electrophoretic mobility was greater than ±1. 5 μm s(-1) V(-1) cm(-1). Changes in the value of the isoelectric point of the complexes with mixing ratio and isothermal titration calorimetric data indicated that complexes formed at pHs 3 and 4 consisted of ∼60 BSA molecules for every GA molecule, while at pH 5 there were ∼10 BSA molecules per GA molecule. Calorimetric studies also indicated that the interaction occurred in two stages at both pH 3 and pH 4, but that the nature of the interaction at these two pH values was significantly different. This was attributed to differences in the relative magnitude of the positive and negative charges on the BSA and GA, respectively, and possibly due to changes in the BSA conformation. The fact that there is an interaction at pH 5, which is above the isoelectric point of the BSA, is due to the interaction of the carboxylate groups on the GA with positive patches on the BSA or to the charge regulation of the protein-polysaccharide system brought about by changes in dissociation equilibria. Complexation is reduced as the ionic strength of the solvent increases and is prevented at a NaCl concentration of 120 mM.

Intermolecular Interactions of IgG1 Monoclonal Antibodies at High Concentrations Characterized by Light Scattering

Light scattering intensity measurements of solutions of two purified monoclonal antibodies were performed over a wide range of concentrations (0.5-275 mg/mL) and ionic strengths (0.02 to 0.6 M). Despite extensive sequence homology between these mAbs, alteration of ∼20 amino acids in the complementarity determining regions resulted in different net intermolecular interactions and responses to solution ionic strength. The concentration dependence of scattering was analyzed by comparison with the predictions of three models, allowing for intermolecular interaction of various types. In order of increasing complexity, the three models account for: (1) steric repulsions (simple hard-sphere model), (2) steric repulsion with short-ranged attractive interactions of varying magnitude (adhesive hard-sphere model), and (3) steric and nonsteric repulsive interactions between several species whose relative concentrations may change as a function of total protein concentration as dictated by equilibrium self-association (effective hard-sphere mixture model). Simple scattering models of noninteracting and adhesive hard-sphere species permitted qualitative interpretation of contributions from excluded volume, electrostatic, and van der Waals interactions on net mAb interactions at high concentration as a function of ionic strength. mAb2 electrostatic interactions were repulsive, whereas mAb1 interactions were net attractive at low ionic strengths, attributed to an anisotropic distribution of molecular charge. The effective hard-sphere mixture model can account quantitatively for the dependence of scattering for both antibodies over the entire concentration range and at salt concentrations exceeding 40 mM. This analysis showed that at high ionic strength both mAbs self-associate weakly to form dimer with an affinity that varies little with salt concentration at concentrations exceeding 75 mM. In addition, mAb1 appears to self-associate further to form oligomers with stoichiometry of 4-6 and an affinity that declines substantially with increasing ionic strength. All three models lead to the conclusion that at high concentrations repulsive interactions are predominantly due to excluded volume, whereas additional features are salt-dependent and reflect a substantial electrostatic contribution to intermolecular interactions of both mAbs.

Phase separation temperatures of a liquid mixture: Dynamic light scattering technique

Abstract Light scattering intensity measurements and photon correlation spectroscopy (PCS) techniques were employed in an investigation of liquid–liquid phase separation behaviour of a mixture of cyclohexane and methanol at seven different compositions. It was found that, except for one composition (29% methanol), the temperature at which the scattering intensity was a maximum did not coincide with the one where the diffusion coefficient was a minimum, as would be for the case of a vapour–liquid system. The difference may be explained in terms of the local density fluctuation and the random walk problem responsible for the peak intensity and the minimum in the diffusion coefficient, respectively. The definition of phase separation temperature, as determined from diffusion process, was also proposed in this work.

Detection of polymeric forms of dihydroquercetin by optical absorption and light scattering

Two methods for the detection of long polymers in dihydroquercetin (DHQ) preparations has been developed. The first method is based on UV spectrophotometry. It was shown that the quantity of long polymers in aqueous solutions can be estimated by the ratio of the absorption bands at 328 and 290 nm, since the 328-nm band was attributed to the monomeric form of DHQ, whereas the 290-nm band was attributed to both the monomeric and polymeric forms. The second method is based on the high-sensitive measurement of light-scattering intensity in aqueous solutions of diluted DHQ preparations using a spectrofluorometer with crossed monochromators. It has been shown that the filtration of DHQ solutions through Millipore filters with a pore diameter of 0.05-0.45 microns makes it possible to nearly completely eliminate long polymers and their aggregates. Long polymers at high concentrations can aggregate. The longest polymers and their aggregates may be 0.1 mm in length, which leads to fluctuations in the light-scattering intensity on the second and minute time scale.

Multiple-scattering effects on static light-scattering optical structure factor measurements

We show that the extent and effect of multiple scattering on angularly resolved light-scattering intensity measurements, the optical structure factor, can be quantitatively described by a single parameter, the average number of scattering events along the scattering volume. This quantity is easily measured or calculated and hence provides a useful experimental indicator of multiple scattering, which is a hindrance to accurate structure factor measurements.

Estimation of Anterior Nucleus of Lens by Scheimpflug Image Before and After Pupil Dilatation

Purpose: To compare the accuracy of lens transparency evaluations by Scheimpflug image in the anterior nucleus of the lens before and after pupil dilatation. Methods: Scheimpflug lens images were recorded in 70 eyes of 38 subjects (age: 28–75 years) before and after pupil dilatation, and light scattering intensity measurements before and after dilatation were compared. Results: There was a significant positive correlation between the light scattering intensity before and after dilatation at the anterior cortex, anterior nucleus, and central clear zone of the lens ( r > 0.9, P < .0001). Conclusions: It is possible to estimate the transparency in the anterior nucleus of the lens from the Scheimpflug image without pupil dilatation. If nuclear type cataracts are regarded as a structural marker of aging in epidemiological studies, measuring the light scattering intensity in the anterior nucleus of the lens without dilatation seems to be a safe, useful, and quantitative method.

Temperature dependence of dynamics of solutions of triblock copolymer in a selective solvent

The temperature dependence of dynamic properties of solutions of a triblock copolymer with polystyrene outer blocks and a middle block of fully hydrogenated polybutadiene (Mw=7.0×104gmol−1, mass fraction of PS 0.28) was studied in a selective solvent for the middle block, n-heptane. In dilute solutions, a gradual decomposition of the flower-like micelles was observed on heating. A more complex behavior was observed in semidilute solutions of the copolymer where three dynamic processes can be reliably extracted from the correlation functions. The fast mode corresponds to the collective diffusion mode of physically interconnected micelles, the broad middle mode is probably due to the tracer diffusion of polydispersed clusters (animal-like structures) formed by random association of the triblock copolymer and the slow mode is probably related to the diffusion of aggregates of insoluble polystyrene impurities. The crossover from relaxational to diffusive behavior was found for samples with c>5.5%(w/v). The scattered light intensity measurements revealed a phase transition for the solution with the concentration 4% (w/v) at a temperature of 79±2°C, which was related to the phase separation of polystyrene homopolymer present in a small amount in the copolymer used.

Dynamics of a Polymer Solution in a Rigid Matrix. 2

Dynamic light scattering measurements of the diffusion coefficient D and the Rayleigh ratio Rθ are reported for dextran molecules confined in agarose gel networks of various concentrations. In this condition, the light scattered by the dextran is some 2 orders of magnitude less intense than that from the agarose. Three molecular weights of dextran were investigated: 7 × 104, 5 × 105, and 2 × 106 g mol-1. For the lowest molar mass it is confirmed that, below the dextran overlap concentration c*, the product DRθ is independent of the agarose concentration, showing that the reduction of the rate of diffusion inside the gel is the result of a decrease in the osmotic pressure in the confined geometry. For the higher molar masses, entanglement effects between the dextran and the network become noticeable in the more highly concentrated gels. The dynamic light scattering intensity measurements are also found to yield reasonable estimates of the molar mass Mw and radius of gyration RG of the trapped dextran molecules. The second virial coefficient A2 is positive, indicating that the agarose−water matrix acts as a good solvent for dextran, but the ratio of RG to the hydrodynamic radius is less than 1.5. These results are interpreted in terms of branching of the dextran molecule.

SANS study of the structure and interaction of L64 triblock copolymer micellar solution in the critical region

Pluronic L64 triblock copolymer is soluble in water at room temperature up to more than 30 wt%, forming disordered spherical micellar phase above the cmc-cmt line. We investigate the structure and interaction between these micelles at temperature approaching the cloud point curve at approximate 57°C along isoconcentration lines. An extensive light scattering intensity measurement indicates that the critical concentration is about 5wt%. We use a previously developed cap-and-gown model for calculating the micellar structure factor and a sticky hard sphere model for the intermicellar structure factor. SANS intensity distribution is fitted with four parameters: the aggregation number of micelle N, the hydrophobic core radius a, the overall hard sphere volume fraction ϕ, and the stickiness between micelles 1/τ. The model is found to describe all SANS data satisfactorily in absolute scale. As one approaches the cloud point curve at constant weight fraction, the aggregation number increases, the micellar core becomes dryer, and the stickiness parameter increases. In particular, at weight fraction of 5%, the stickiness parameter approaches the critical value 10.2 at T=330.9 K. We thus conclude that there is a critical demixing point in this micellar solution where micelles interact strongly with each other by a short range temperature dependent attraction.

Forces acting on particle-enhanced immunoassays

The aim of the present work is to study the role of the different forces involved in the agglutination of immune γ-globulin (IgG) covered latex particles due to antigen-antibody reaction. An experimental investigation on the adsorption of IgG molecules on three latexes with different surface charge densities is described. Photon correlation spectroscopy was used to determine the hydrodynamic layer thickness of the IgG molecules adsorbed on the latexes. In order to get an insight into the forces acting between two antibody-covered particles approaching each other, the colloidal stability and immunoreactivity of these biocomplexes were studied. They can be stabilized by electrostatic or hydration forces. The immunological agglutination of IgGimmobilized latex particles due to the addition of the antigen was quantified through scattered light intensity measurements. The immunoresponse increases with ionic strength of the medium until a maximum value is achieved. Above this maximum, the immunoreactivity decreases.

Cholic acid behavior in water and organic solvent: study of normal and inverted aggregates

Water-soluble fluorescent probes, including 1-pyrene butyric acid, rhodamine B, sodium salt 1,5-diaminoanthraquinone-2,6-disulfonic acid, quinine hemisulfate and monosodium salt 8-amino-1-naphthol-3,6-disulfonic acid were used to determine the critical micelle concentration (cmc) of inverted micelles formed by cholic acid in tetrahydrofuran. Another water-insoluble fluorescent probe, namely pyrene, was used to determine the cmc of normal micelles formed by sodium cholate in water. Relative scattered light intensity measurements give direct evidence of transition concentrations similar to cmc in surfactants. Our results indicate that in the inverted micelles, hydrophilic sites placed in the core are present in cholic acid aggregates above the cmc region at 5–7 mM. In normal micelles, hydrophobic sites in the core are present in sodium cholate aggregates above the cmc region at 15 mM. Another critical point in the aggregation of cholic acid and sodium cholate occurs at 1 mM. Normal phase liquid chromatography determination of the cmc reversed micelles has also been performed, and the results obtained agree well with the spectroscopic studies.

Dynamics of a Polymer Solution in a Rigid Matrix

Dynamic light scattering measurements of the diffusion coefficient D and the Rayleigh ratio R θ are reported for dextran molecules confined in agarose gel networks of various concentrations. In this condition, the light scattered by the dextran is some 2 orders of magnitude less intense than that from the agarose. Three molecular weights of dextran were investigated: 7 x 10 4 , 5 x 10 5 , and 2 x 10 6 g mol -1 . For the lowest molar mass it is confirmed that, below the dextran overlap concentration c * , the product DR θ is independent of the agarose concentration, showing that the reduction of the rate of diffusion inside the gel is the result of a decrease in the osmotic pressure in the confined geometry. For the higher molar masses, entanglement effects between the dextran and the network become noticeable in the more highly concentrated gels. The dynamic light scattering intensity measurements are also found to yield reasonable estimates of the molar mass M w and radius of gyration R G of the trapped dextran molecules. The second virial coefficient A 2 is positive, indicating that the agarose-water matrix acts as a good solvent for dextran, but the ratio of R G to the hydrodynamic radius is less than 1.5. These results are interpreted in terms of branching of the dextran molecule.

Thermodynamics of Crew-Cut Micelle Formation of Polystyrene-b-Poly(acrylic acid) Diblock Copolymers in DMF/H2O Mixtures

The thermodynamics of formation of “crew-cut” micelles of polystyrene-block-poly(acrylic acid) (PS-b-PAA) diblock copolymers were investigated. The PAA/PS ratios were in the range 0.08−0.33, and N,N-dimethylformamide/water (DMF/H2O) mixtures were used as the selective solvent. For the block ratios investigated here, the copolymers form spherical crew-cut micelles with a large PS core and a thin PAA corona. The temperature dependence of the critical micelle concentration (cmc) was determined under different conditions from scattered light intensity measurements as a function of temperature. The closed association model was found to describe the micellization process and was used to calculate the standard Gibbs free energies (ΔG°), the standard enthalpies (ΔH°), and the standard entropies (ΔS°). The effects of solvent composition, copolymer composition, and added NaCl content on the thermodynamic functions were studied. From the experimental data, a single set of combined equations for the standard thermody...

Characterization of iron oxide-silica nanocomposites in flames: Part II. Comparison of discrete-sectional model predictions to experimental data

A discrete-sectional model accounting for particle formation by chemical reaction and growth by coagulation and condensation is developed to predict the evolution of the nanocomposite aerosol size distribution in a multicomponent iron-silicon system in a flame. Particle formation by nucleation of the vapor is represented by an Arrhenius-type rate expression, with the rate constant being obtained from experiments and simulation results reported in the literature. Precursor vapor concentrations and the second aerosol volume moment predictions are compared to laser-induced fluorescence (LIF) and light scattering intensity measurements from experiments described in Part I20 of the paper. The results elucidate the important formation and growth mechanisms of nanocomposite ferric oxide-silica particles in flame reactors. The role of operating parameters such as precursor characteristics and temperature profiles on the final product characteristics is established.

Aerodynamic Particle Sizing versus Light Scattering Intensity Measurement as Methods for Real-Time Particle Sizing Coupled with Time-of-Flight Mass Spectrometry

Measurement of scattered light intensity and aerodynamic particle sizing are two methods that have recently been coupled with time-of-flight mass spectrometry for real-time determination of aerosol particle size and composition. An aerosol analysis technique recently developed in our laboratory, aerosol time-of-flight mass spectrometry, offers a unique experimental platform to evaluate both of these sizing techniques. This paper presents a comparison of results obtained with these two methods.

Dimethyl sulfoxide cataract: a model for optical anisotropy fluctuations

Rat lenses incubated in dimethyl sulfoxide (DMSO)–water binary mixtures of different compositions became turbid. A slight haziness developed up to 0.062 mole fraction of DMSO; at higher concentrations dense turbidity developed. Microscopic examination of the incubated rat lenses showed damage restricted to the epithelium and outer cortex at low DMSO concentrations; maximum damage occurred, in terms of fiber cell swelling, extracellular fluid (lake) formation and disintegration of epithelium, at 0.25 mole ratio of DMSO. Scanning electron microscopic observation showed that at high DMSO concentrations, especially at 0.25 mole fraction, the contents of the fiber cells were greatly damaged. Apparently a large part of the crystallins had coalesced around the cytoskeletal bodies. Polarized light-scattering intensity measurements and their analyses indicated that when dense opacities developed at high DMSO concentrations, the major contribution to the turbidity came from the optical anisotropy fluctuations. The change in the organization of the components within the fiber cells disturbs the balance between intrinsic birefringence and form birefringence necessary for transparency. Thus, the DMSO-caused opacification can be described as a good model for the involvement of optical anisotropy fluctuations in cataractogenesis.